1. Field of the Invention
The present invention relates generally to a light head structure with adjustable focal length and a lighting device thereof. The light head structure includes a soft lens. The thickness of the soft lens is adjustable to change the focal length and enhance the illumination. The lighting device can be easily manufactured to lower manufacturing cost.
2. Description of the Related Art
A flashlight is a portable lighting device, which is often used outdoors or as an emergency lighting device in a blackout. The projection range of a common flashlight is unadjustable as desired. This is inconvenient when it is necessary to change the scattering angle of the flashlight. Therefore, an improved flashlight with adjustable focal length has been developed to solve the above problem.
The conventional lighting device (flashlight) with adjustable focal length includes a light head and a barrel body mated with the light head. An optical lens is disposed in the light head. The light head can be rotated up and down to adjust the distance (focal length) between a light-emitting element (such as an LED) and the lens. When a user needs to illuminate a nearby place, the user can turn the light head downward in a direction to the barrel body so as to shorten the distance between the light-emitting element and the lens. In this case, the light emitted from the light-emitting element will pass through the lens and scatter. On the contrary, when the user needs to illuminate a remote place, the user can turn the light head upward in a direction away from the barrel body so as to elongate the distance between the light-emitting element and the lens. In this case, the light emitted from the light-emitting element will pass through the lens and converge.
Such conventional lighting device is able to achieve a zoom effect. However, when manufacturing the lighting device, it is necessary to manufacture a specific optical lens with a specifically developed mold for projecting the light of the light-emitting element to a preset range. Accordingly, the application range of the lighting device is quite narrow. Moreover, due to the zoom structure, the lighting device is complicated as a whole.
Furthermore, when changing the optical design of the lighting device in adaptation to the market or on the demand of a client, it is necessary to redesign the optical lens and redevelop a new mold. This leads to increase of cost and working time.
According to the above, the conventional lighting device has the following shortcomings:
1. The cost is increased.
2. The structure is complicated.
3. The working time is prolonged.